The present invention relates generally to an automatic speed control system for an automotive vehicle, a so-called "cruise control" system for maintaining the vehicle speed at a desired and pre-set constant value. More specifically, the invention relates to an automatic speed control system having therein an accelerator switch for resetting and renewing the pre-set value in the system and a means for preventing the vehicle from unnecessarily and uncontrollably accelerating by maintaining the accelerator switch in position.
Various kinds of automatic speed control systems for automatically controlling the vehicle speed at a pre-set constant value have been developed. Such devices are known as "cruise control systems" and are useful for driving the vehicle for relatively long periods of time at a constant speed. Generally, the automatic vehicle speed control system is provided with a means for setting a vehicle speed at a desired value to control the vehicle speed thereto. While the control system is in operative and therefore controls the vehicle speed at a pre-set constant value, the control system becomes inoperative if a vehicle brake is applied or if a clutch is disengaged by operating the clutch pedal or by setting the transmission lever to the neutral position. On the other hand, if the vehicle's accelerator is depressed, thus causing an accelerator switch to be turned on while the control system is operating to control the vehicle speed, the pre-set value in the system is cleared and the vehicle speed is accelerated at a given rate for so long as the accelerator switch is maintained in its ON position. Upon releasing the accelerator, thereby turning off the accelerator switch, the vehicle speed at that time is set as a renewed pre-set value.
In such automatic speed control systems, a disadvantage has been expected that, if the accelerator switch is damaged while it is turned on, and therefore it can not return to its OFF position, the vehicle is accelerated uncontrollably responsive thereto by the control system. This will necessarily cause danger for the vehicle since the vehicle speed is unexpectedly and uncontrollably accelerated to the maximum speed thereof. By application of the brake and turning off the power supply to the control system, acceleration of the vehicle (caused by maintaining the accelerator switch ON) can be temporarily stopped and the vehicle can be decelerated to a safe speed. However, once the brake is released, the control system returns to its operative mode to continue to accelerate the vehicle due to the ON position of the accelerator switch.
Therefore, the present invention provides a fail-safe system for an automatic vehicle speed control system for preventing the vehicle from unnecessarily and uncontrollably accelerating even when the system is damaged and is kept in an accelerating mode.